Process of making a lightweight thermal heat transfer apparatus

ABSTRACT

A lightweight thermal heat transfer apparatus, including a core section and a laminate composite section. The core section is substantially similar to a diamond shape. The laminate composite section has a plurality of thermally conductive fibers, which are disposed around the core section and oriented at a configuration similar to the core section.

CROSS REFERENCES

This application is a division of application Ser. No. 10/056,812, filedJan. 24, 2002 now U.S. Pat. No. 7,156,161, entitled Lightweight ThermalHeat Transfer Apparatus.

STATEMENT OF GOVERNMENT INTEREST

The invention described herein may be manufactured and used by or forthe Government of the United States of America for governmental purposeswithout payment of any royalties thereon or therefor.

BACKGROUND

The present invention relates to a lightweight thermal heat transferapparatus, which provides an efficient thermal conduction path from athermal source. More specifically, but without limitation, the presentinvention relates to a lightweight thermal heat transfer apparatus thatcan function either as a heatsink and/or a heat dissipative fin that canbe used in conjunction with electronic equipment.

A heatsink, a heat dissipative fin and/or a thermal heat transferapparatus is typically, but without limitation, an apparatus which hashigh thermal conductivity and lowers the temperature as well as drawsheat from a thermal source. Typically a heat sink, a heat dissipativefin and/or a thermal heat transfer apparatus dissipates, scatters,disperses heat, or even makes heat disappear. A heatsink, a heatdissipative fin, and/or a thermal heat transfer apparatus also providesa thermal conductive path away from a thermal source.

Heat sinks, heat dissipative fins and/or thermal heat transferapparatuses are widely used in the electronics industry to providepassive thermal control of electronic components. Aluminum, copper andother metals or metal alloys have been used for these applications.However, as electronic components have decreased in size, power densityhas increased. These factors have resulted in higher heat dissipationrequirements in electronic components than conventional materials anddesigns can provide. The power levels and power densities of manycurrent electronic designs are limited by the heat dissipativecapabilities of their heatsinks, heat dissipative fins and/or thermalheat transfer apparatuses.

For a variety of electronic applications, such as aircraft or aerospaceapplications, it is highly desirable to minimize the weight of theheatsink, the heat dissipative fin and/or the thermal heat transferapparatus and maximize its heat dissipative capabilities.

Laminated composites have been used to manufacture heatsinks, heatdissipative fins and/or thermal heat transfer apparatuses. The use oflaminated composites, composed of fibers and a matrix material, as heatsinks, heat dissipative fins and/or thermal heat transfer apparatuseshas not resulted in as much thermal conductivity as was originallyanticipated because the transverse thermal conductivity of these fibersis an order of magnitude less than axial thermal conductivity. Thusthere is a requirement for a new thermal heat transfer apparatus thatprovides a direct thermal path along the fiber axis from the surface ofthe thermal heat transfer apparatus to its edge. This requirement wouldprovide more thermal conductivity and minimize weight and size of theheatsink, heat dissipative fin and/or thermal heat transfer apparatus.

For the foregoing reasons, there is a need for a lightweight thermalheat transfer apparatus. Information relevant to attempts to addressthese problems can be found in U.S. Pat. Nos. 4,609,586, 4,849,858,4,867,235, 4,888,247, 5,002,715, 5,111,359, 5,287,248, 5,255,738,5,224,030, and 5,316,080. (None of these patents are admitted to beprior art with respect to the present invention.) However, each of thesereferences suffers from one of the above listed disadvantages.

SUMMARY

The present invention is directed to a lightweight thermal heat transferapparatus that satisfies the needs listed above and below.

It is an object of the present invention to provide a lightweightthermal heat transfer apparatus that includes a core section and alaminate composite section. The core section may be substantiallydiamond shaped. The laminate composite section has a plurality ofthermally conductive fibers. The thermally conductive fibers aredisposed around the core section and are oriented at a configurationsimilar to the core section.

It is an object of the present invention to provide a lightweightthermal heat transfer apparatus that transfers heat multidirectionallyaway from an apparatus that generates heat.

It is an object of the present invention to provide a lightweightthermal heat transfer apparatus that is lightweight and an effectivethermal conductor.

It is an object of the present invention to provide a lightweightthermal heat transfer apparatus that can be used as either a heatsink, aheat dissipative fin or as a cooling fin, or in other applications wherethermal conduction is required of a plate-shaped conduit.

It is an object of the present invention to provide a lightweightthermal heat transfer apparatus that provides a configuration in whichheat flux is relatively constant along paths through the lightweightheat transfer apparatus.

It is an object of the present invention to provide a lightweightthermal heat transfer apparatus that provides a direct thermal pathalong the fiber axis from the surface of the lightweight thermal heattransfer apparatus to its edges.

DRAWINGS

These and other features, aspects and advantages of the presentinvention will become better understood with reference to the followingdescription and appended claims, and accompanying drawings wherein:

FIG. 1 is a cross sectional view of a lightweight thermal heat transferapparatus;

FIG. 2 is a cross sectional view of a lightweight thermal heat transferapparatus with increased fiber intersect angles;

FIG. 3 is a cross sectional view of a lightweight thermal heat transferapparatus with plies; and

FIG. 4 is a cross sectional view of a lightweight thermal heat transferapparatus with a stiffener.

DESCRIPTION

The preferred embodiment of the present invention is illustrated by wayof example in FIGS. 1, 2, 3 and 4. As shown in FIGS. 1, 2, 3 and 4 thelightweight thermal heat transfer apparatus 1 includes a core section 10and a laminate composite section 20.

A laminate composite typically contains two or more interconnected thinlayers, stratum, lamella, membranes, plates, folds, wafers, or the like.The laminate composite section 20 may have a plurality of thermallyconductive fibers 22. Fibers are typically, but without limitation,threadlike structures, ropelike structures, or slender filaments thatcombine with others to form a substance and/or very fine continuousstrands. Thermally conductive fibers 22 are fibers that have the abilityto transmit, conduct, transport, carry to or take from one place toanother, transfer or convey heat. The plurality of thermally conductivefibers 22 may be imbedded in a matrix. The matrix material may be apolymer or a polymer with metallic and/or thermally conductivechopped-fiber additions. A polymer is typically defined, but withoutlimitation, as a compound of high molecular weight derived either by theaddition of many smaller molecules or by condensation of many smallermolecules with the elimination of water, alcohol, or the like. Thematrix material may also be of a metallic or ceramic composition. Thelightweight thermal heat transfer apparatus 1 may also include off-axisthermally conductive fibers 22 that are both continuous anddiscontinuous to aid heat flow across the principal fiber directions.

The thermally conductive fibers 22 may be isotropic (having similarproperties in every direction), or anisotropic (having differentproperties in different directions). Thermally conductive fibers 22 thatare anisotropic and made from mesophase pitch material are preferred. Amesophase pitch material is defined as, but without limitation, amaterial created from a form of tar or pitch (a heavy liquid or darkresidue obtained by the distillation of tar) followed by repeatedstretching and exposure to elevated temperatures to convert the materialto graphite fibers that are in an intermediate, nematic (being in aphase characterized by arrangement of long axes in parallel lines butnot layers) or smectic (being in a phase characterized by arrangement ofmolecules in layers with long molecular axes) stage. Exposuretemperatures could be as high as about 3500 degrees Celsius in an inertatmosphere. Thermally conductive fibers 22 made from mesophase pitchmaterial typically assume a two-dimensional graphitic crystallinestructure along the fiber axis, and posses thermal conductivitiesranging from about 100 to about 1100 W/m degrees Kelvin and have adensity of about 2 to about 2.5 g/cc. The thermal conductivities ofthermally conductive fibers 22 manufactured from mesophase pitchmaterial are typically 2-3 times greater then the thermal conductivitiesof copper, a material often used in applications where high thermalconductivities are required. The thermally conductive fibers 22manufactured from mesophase pitch material also posses extremely highmoduli (about 100×10(to the 6^(th) power) psi, modulus is typicallydefined as the measure of a force or properties of mass or theireffects), and also posses high strength (about 300 ksi).

The thermally conductive fibers 22 may also be made from carbon fiber. Athermally conductive fiber 22 made from carbon fiber is produced frompolyacrylonitrile (PAN) and is stretched and exposed to elevatedtemperatures as high as about 2500 degrees Celsius. Thermally conductivefibers 22 made from carbon fiber have thermal conductivities rangingfrom about 10 to about 70 W/m degrees Kelvin. They also posses highstrength (about 400 to about 500 ksi), and high moduli (about 40 toabout 50×10(to the 6^(th) power) psi). The thermally conductive fibers22 made from carbon fiber typically have a density of about 1.8 g/cc.

Metallic additions to the thermally conductive fibers 22 may be added,and also may be in the form of coatings. Metallic additions may bedispersed in the matrix and may be in the form of flakes, choppedfibers, lenticular shapes, and the like. Thermally conductive fibers mayalso be added in the translaminar (through-thickness) direction tofurther aid in heat dissipation. These fibers could be discontinuous anddispersed in the matrix or continuous and inserted through the thicknessof the laminate.

The laminate composite section 20 may be produced using compressionmolding, oven or autoclave operations, resin transfer molding or anyother method compatible with fabrication of such a polymeric matrixconfiguration.

The thermally conductive fibers 22 may be supported by pitched-basedfibrous reinforcements. The pitched-based fibrous reinforcements aretypically an added piece, a support, a material, or an apparatus, deviceor system that strengthens the thermally conductive fibers 22. Thepitched-based fibrous reinforcements can be made from material similarto the thermally conductive fibers 22; however, the pitched-basedfibrous reinforcements are shaped in a manner to effectively reinforcethe thermally conductive fibers 22. An example would be a triangle shapein apex regions of the core section 10 or a variety of shapes used forsimilar purposes dependent on the interior or core section 10 spacegeometry. The volume occupied in these core section 10 regions would befurther dependent on the degree of reinforcement required.

A core section 10 is typically the central part of a heat transferapparatus. The thermally conductive fibers 22 may be disposed around thecore section 10. The core section 10 may be a variety of shapes. Thepreferred shape of the cross sectional area of the core section 10 issubstantially similar to a diamond shape. A diamond shape can include,but without limitation, a lozenge or a rhombus shape. A rhombus istypically an equilateral parallelogram, especially one with oblique orslanting angles. A lozenge is typically a four-sided equilateral figurewhose opposing angles are equal. The core section 10 may contain coreedges or a core interface 16. The core edges or core interface 16 is thesurface regarded as the common boundary of the core section 10 and thelaminate composite section 20 or the thermally conductive fibers 22. Thecore edges or core interface 16 may be straight lines, curved or arcedlines. The curvature of the core edges or core interface 16 may behyperbolic, parabolic, or any type of curvature. The curvature of thecore edges or core interface 16 may be changed to optimize the volume ofthe thermally conductive fibers 22 to suit the needs of the application.In the preferred embodiment, the thermally conductive fibers 22 areorientated at a configuration similar to the core section 10. The coresection 10 may have four core section sides 12 and four core sectionapexes 14 (pointed ends or tips). The four core section sides 12 make upthe core edges or core interface 16. As shown in FIG. 1, each coresection side 12 may have a plurality of thermally conductive fibers 22parallel to it. In another embodiment of the invention, as shown in FIG.2, the thermally conductive fibers 22 may have an increased fiberintersect angle. In this embodiment, the thermally conductive fibers 22may be curved, rounded, hyperbolic, parabolic, ellipsoidal, arced or beshaped as a part of a circle and not aligned as a straight line. Inanother embodiment, the curvature of the core section sides 12 can besubstantially varied to correspond to functions such as X, X², X³,e^(x), etc.

The lightweight thermal heat transfer apparatus 1 can be substantiallysimilar to the shape of a parallelogram, while the cross sectional areamay also be substantially similar to the shape of a parallelogram. Aparallelogram is typically defined as a four-sided plane figure havingthe opposite side parallel and equal. A parallelogram may include, butis not limited to, a square, a rectangle, and a rhomboid. A rectangle istypically a four-sided plane figure with four right angles, while asquare typically has four equal sides and four right angles. Thelightweight thermal heat transfer apparatus 1 has edges 30, borders ormargins as defined by its shape. These edges 30 may be straight, arced,curved or rounded. The edges 30 may also be the exterior or externallaminate or exterior or external thermally conductive fibers 22 orlaminate composite section 20.

In one of the many possible embodiments, the edges 30 of the lightweightthermal heat transfer apparatus 1 are coated with a conductive coating40. A coating is defined, but without limitation, as a layer of anysubstance spread over a surface. The conductive coating 40 may be acoating of pure metal or an alloy. A metal is typically, but withoutlimitation, defined as an electropositive chemical element characterizedby ductility, malleability, luster, conductivity of heat andelectricity. An alloy is typically defined, but without limitation, as amixture of two or more metallic elements or non-metals which has ametallic appearance and/or some metallic properties. Copper, nickel,silver, gold, aluminum, alloys of these metals, as well as variouscombinations such as copper molybdenum, boron nitride andberyllium-aluminum can be used as conductive coatings. Diamond coatingsmay also be used as a conductive coating 40 because of their super highconductivity. A diamond coating may be defined, but without limitation,as a coating made from a crystalline carbon which typically containscolorless or tinted isometric crystals. The diamond coating may be madefrom a naturally occurring, industrial or synthetic crystalline carbon.The conductive coating 40 should posses good thermal conductivity andhave reasonable adherence to the edges 30 of the lightweight thermalheat transfer apparatus 1. Coating an edge 30 of the lightweight thermalheat transfer apparatus 1 provides a conductive path for off axis fibersfrom the side wedge (any surface of the interior) to the cold-wall edge(those surfaces where the ends of the thermal conducting fibersterminate). A coated cold-wall edge will insure intimate contact withall the conductive fiber ends at the edge of the laminate. This willprevent localized degradation in thermal performance.

The thermally conductive fibers 22 may be disposed at non-zero,non-right angles or oblique (neither perpendicular nor parallel to agiven line or surface) angles to the edges 30 of the lightweight thermalheat transfer apparatus 1. In the preferred embodiment, the thermallyconductive fibers 22 are disposed at an angle to the edges 30 and noneof the thermally conducted fibers 22 are parallel or perpendicularlyorthogonal (at a right angle) to any of the edges 30.

The core section 10 may be hollow. The core section 10 may be a materialselected from the group of air, foam, fluid and/or honeycomb. The foamor honeycomb may be polymeric or metallic in nature, with additions ofthe opposite material in the case of the foam to enhance desiredproperties. Such an approach allows for significant weight savings,approximately 33% over a conventionally configured (without alightweight core) composite. The core section 10 may also be made from asolid polymeric based system of materials, which is a group of materialswhereby the primary material is a polymer mixed in with other materials.Both thermoset (rendered hard by heat) and thermoplastic (rendered softand moldable by heat) polymeric materials could be used to make the coresection 10. The polymeric based core section 10 may be manufacturedusing injection molding, compression molding, extrusion, oven orautoclave curing operations, resin transfer molding, vacuum assistedresin transfer molding, or any other type of manufacturing process thatlends itself to producing a polymeric based system of materials. Thepolymeric-based foam or solid core options could also employ continuousas well as discontinuous thermally conductive fibers. Metallic additionsto the polymers may be used to further improve thermal conductivity. Themetallic additions to the polymer-based core section 10 may be in theform of flakes, chopped fibers, lenticular shapes, or coatings orgraphite fibers, and the like. Metallic additions irrespective of formwould enhance transverse fiber conductivity.

If a hollow configuration is used, additional thermal dissipation may beachieved by fluid convection. Convection is typically defined, but notlimited to, a movement of parts of a fluid within the fluid because ofdifferences in heat, and heat transference by such movement. Fluids aretypically either liquid or gas. By forcing air or other fluids through ahollow core section, additional heat flow may be realized. A number offluids can be used to effect thermal transport. Aqueous-based liquidswith additives such as ethylene glycol, petroleum-based fluids andsilicone-based fluids are a few examples of the many types of differentfluids that may be used to realize additional heat flow. Additives arealso effective in retarding oxidation and degradation as well asenhancing thermal efficiency. The selection of a particular fluid wouldbe dependent on the thermal service conditions, among other factors.

Stiffening an apex 14 of the core section 10 may be required to meet thestructural requirements of some applications. The apexes 14 may bestiffened by adding a plurality of plies 50. The plurality of plies 50may be added to a pair of opposite or across from each other apexes 14of the core section 10. A ply 50 is typically, but without limitation, athickness or layers of material in a particular area. The plies 50 canbe additional layers of thermally conductive fibers 22 that give thelocal area support. The lightweight thermal heat transfer apparatus 1may contain several groups of plurality of plies 50. The groups may beplaced at each individual apex 14. As shown in FIG. 3, the preferredembodiment includes two groups of a plurality of plies 50, one group ofthe plurality of plies 50 is attached at one apex 14, and the othergroup of plurality of plies 50 is attached at an opposite apex 14.

The lightweight thermal heat transfer apparatus 1 may also include astiffener 60 to allow support for the thermally conductive fibers 22 andto maintain the shape of the core section 10. The stiffener 60 mayinclude a stiffener shaft portion 62 and two stiffener supports 64 onopposite ends of the stiffener shaft portion 60. As shown in FIG. 4, thetwo stiffener supports 64 may be disposed at opposite apexes 14. Thestiffener 60 may be substantially I-shaped with a top line 66 and abottom line 68. The top line 66 and the bottom line 68 may be the twostiffener supports 64. The two stiffener supports 64 may slope or angledownward or upward at the stiffener shaft portion 62. The stiffener topline 66 and bottom line 68 (each respective stiffener support 64)correspond to the thermally conductive fibers 22. The stiffener 60 maybe manufactured from any metal, metal alloy, plastic, ceramic, rubber orany type of material. The stiffener 60 may be produced from thethermally conductive fibers 22. This type of configuration would promotewhat is known to one skilled in the art as Z-direction heat transfer.The stiffener 60 may be manufactured from carbon fiber-reinforcedpolymeric composites, graphite fiber-reinforced polymeric composites, ora composite of fiber with metal or plastic or both. Metallic additionsmay be used in the stiffener to improve thermal conductivity properties.

The geometry shown in the lightweight thermal heat transfer apparatus 1uses more conductive material where, in a conventional heatsink, theheat flux is large. Similarly it uses less material when the heat fluxis normally small. Heat flux is typically an indication of the thermaltransport for specific configurations and their boundary conditions.Heat flux is proportional to the change in temperature with respect todistance. In a steady state condition, heat flux of a conventional heatsink is greatest at its edge and a minimum at its center. The geometryof the lightweight thermal heat transfer apparatus 1 provides aconfiguration in which heat flux is relatively constant along an axisthrough the lightweight heat transfer apparatus 1. The geometry alsoprovides a direct thermal path along the fiber axis from the surface ofthe lightweight thermal heat transfer apparatus 1 to its edge 30.

The lightweight thermal heat transfer apparatus 1 may be constructedusing many various fabrication techniques. One such technique is byfabricating an oval with the thermally conductive fibers 22. The oval isthen cut into quadrants. The quadrants are aligned around asubstantially diamond shaped core section 10 such that the diamond shapeis maintained. Another possibility is by building the laminateply-by-ply or fiber-by-fiber and staggering the ply lengths to permitouter skin laminate to exhibit a half diamond-like shape. A core section10 could then be bonded to the two such laminates resulting in thepreferred embodiment of the present invention. The core section 10 maybe manufactured using any method that provides the designed coregeometry. One method is to fabricate the core section 10 fromlow-density foam, which collapses when pressure is applied duringprocessing, yet still, maintains its diamond shape. Another method is tomachine a core section 10 from a larger piece of foam or material.

Although the present invention has been described in considerable detailwith reference to certain preferred versions thereof, other versions arepossible. Therefore, the spirit and scope of the appended claims shouldnot be limited to the description of the preferred versions containedherein.

Any element in a claim that does not explicitly state “means for”performing a specified function, or “step for” performing a specificfunction, is not to be interpreted as a “means” or “step” clause asspecified in 35 U.S.C. 112 paragraph 6. In particular, the use of “stepof” in the claims herein is not intended to invoke the provisions of 34U.S.C. 112 paragraph 6.

1. A manufacturing process of making A lightweight thermal heat transfer apparatus comprising the steps of: (a) fabricating an oval with thermally conductive fibers; (b) cutting the oval into quadrants; and (c) aligning the quadrants around a substantially diamond shaped core section such that the substantially diamond shape of the core section is maintained.
 2. The process of claim 1, wherein the thermally conductive fibers are manufactured from a mesophase pitch material, the mesophase pitch material is prepared by (a) distilling pitch, and (b) repeated stretching and exposure to temperature as high as 3500 degrees Celsius until the pitch is converted to graphite fibers that are in an intermediate stage.
 3. The process of claim 2, wherein the mesophase pitch material has a density in a range of about 2 to about 2.5 g/cc.
 4. The process of claim 3, wherein the mesophase pitch material has a thermal conductivity in a range of about 100 to about 1100 W/m degrees Kelvin.
 5. The process of claim 1, wherein the thermally conductive fibers are manufactured from carbon fiber.
 6. The process of claim 5, wherein the carbon fiber has a density of about 1.8 g/cc.
 7. The process of claim 6, wherein the carbon fiber has a thermal conductivity in a range of about 10 to about 70 W/m degrees Kelvin. 